Fix (Blanks) selection for empty string (#4914)

* test(filtering): add test for issue #4875

* fix(filtering): fix blanks for empty string #4875

* test(filtering): remove detectChanges, fix test name #4875

Author: DiyanDimitrov

projects/igniteui-angular/src/lib/grids/filtering/excel-style/grid.excel-style-filtering.component.ts

@@ -316,6 +316,14 @@ export class IgxGridExcelStyleFilteringComponent implements OnDestroy, AfterView
             return true;
         }
 
+        if (this.filterValues.size === 1) {
+            const firstValue = this.filterValues.values().next().value;
+
+            if (!firstValue && firstValue !== 0) {
+                return true;
+            }
+        }
+
         for (let index = 0; index < this.uniqueValues.length; index++) {
             if (this.filterValues.has(this.uniqueValues[index])) {
                 return true;

projects/igniteui-angular/src/lib/grids/grid/grid-filtering-ui.spec.ts

@@ -3930,6 +3930,25 @@ describe('IgxGrid - Filtering actions - Excel style filtering', () => {
             [ true, true, true ]);
     }));
 
+    it('Should select (Blanks) when the blank value is empty string.', fakeAsync(() => {
+        grid.data[0].AnotherField = '';
+        fix.detectChanges();
+
+        openExcelMenu(fix, 5);
+        verifyExcelStyleFilterAvailableOptions(grid,
+            [ 'Select All', '(Blanks)', 'a', 'custom' ],
+            [ true, true, true, true ]);
+
+        toggleExcelStyleFilteringItems(fix, grid, true, 2, 3);
+
+        expect(grid.rowList.length).toBe(1);
+
+        openExcelMenu(fix, 5);
+        verifyExcelStyleFilterAvailableOptions(grid,
+            [ 'Select All', '(Blanks)', 'a', 'custom' ],
+            [ null, true, false, false ]);
+    }));
+
     it('Should display the ESF based on the filterIcon within the grid', async() => {
         // Test prerequisites
         grid.width = '800px';